Solid state transducer (“SST”) devices are used in a wide variety of products and applications. For example, mobile phones, personal digital assistants (“PDAs”), digital cameras, MP3 players, and other portable electronic devices utilize SST devices for backlighting. SST devices are also used for signage, indoor lighting, outdoor lighting, and other types of general illumination. SST devices generally use light emitting diodes (“LEDs”), organic light emitting diodes (“OLEDs”), and/or polymer light emitting diodes (“PLEDs”) as sources of illumination, rather than electrical filaments, plasma, or gas. FIG. 1A is a cross-sectional view of a conventional SST device 10a with lateral contacts. As shown in FIG. 1A, the SST device 10a includes a substrate 20 carrying an LED structure 11 having an active region 14, e.g., containing gallium nitride/indium gallium nitride (GaN/InGaN) multiple quantum wells (“MQWs”), positioned between N-type GaN 15 and P-type GaN 16. The SST device 10a also includes a first contact 17 on the P-type GaN 16 and a second contact 19 on the N-type GaN 15. The first contact 17 typically includes a transparent and conductive material, e.g., indium tin oxide (“ITO”), to allow light to escape from the LED structure 11. In operation, electrical power is provided to the SST device 10a via the contacts 17, 19, causing the active region 14 to emit light.
FIG. 1B is a cross-sectional view of another conventional LED device 10b in which the first and second contacts 17 and 19 are opposite each other, e.g., in a vertical rather than lateral configuration. During formation of the LED device 10b, a growth substrate (not shown), similar to the substrate 20 shown in FIG. 1A, initially carries an N-type GaN 15, an active region 14 and a P-type GaN 16. The first contact 17 is disposed on the P-type GaN 16, and a carrier 21 is attached to the first contact 17. The substrate is removed, allowing the second contact 19 to be disposed on the N-type GaN 15. The structure is then inverted to produce the orientation shown in FIG. 1B. In the LED device 10b, the first contact 17 typically includes a reflective and conductive material, e.g., silver or aluminum, to direct light toward the N-type GaN 15. An optional converter material and an encapsulant can then be positioned over one another on the LED structure 11. In operation, the LED structure 11 can emit energy at a first wavelength, e.g., blue light, that stimulates the converter material, e.g., phosphor, to emit energy at a second wavelength, e.g., yellow light. Energy at the first and second wavelengths is combined to generate a desired color of light, e.g., white light.
Conventional SST devices are made with a single, monolithic light delivery surface that receives a single voltage input and provides a single output across the lighting surface. Due to inherent manufacturing inconsistencies, the light output and efficiency of a given device may vary from one device to another, or within a given device. For example, the light output from devices made from a single wafer can vary as a function of the distance between the device and the center of the wafer or the edge of the wafer. For particular dies, e.g., large dies, the light output can vary across the surface of a single die, producing undesirable output variations.
Some conventional SST devices incorporate a die-level lens, such as a spotlight lens, that focuses or otherwise alters light output. A conventional monolithic lighting device, however, may produce light outside the lens area, which is not focused. Accordingly, conventional solid state transducer devices with die-level lenses are generally less than optimally efficient. Another drawback with conventional monolithic solid state transducer devices is the difficulty associated with controlling the heat generated in the device. During normal conditions, the lighting device may heat up irregularly due to manufacturing inconsistencies in the die itself, or due to the environment in which the device is employed. The typical response to excessive heating is to switch off the lighting device to avoid damaging it. However, this defeats the operational purpose of the device. Accordingly, there is a need in the art for an improved SST device.